Let’s say you’re taking a math test. There are 50 questions and you get five wrong. In some schools, that’s good enough for an A. Not too shabby.

Now take that test out to the football field, where you’re a defensive back responsible for locking down the other team’s best receiver.

“Say there’s 50 plays in a football game and you don’t make five plays,” Huntley defensive backs coach Casey Popenfoose said. “That’s a 90 percent on a test, but you can lose a ballgame with that. That could be five touchdowns.”

For this reason, defensive back is the most difficult position on the football field. Well ... at least according to Popenfoose, a 2008 Huntley graduate who went on to play cornerback and safety at NCAA Division II Upper Iowa University.

“You have a lot of responsibility,” he said. “If you’re doing your job, you’re not noticed (because the offense isn’t throwing the ball your way.) But if you screw up once, it can be a touchdown.”

Before we throw you out on the field for final exam, let's first hit the books — the playbook that is — to examine the basics.

For football newcomers, a defensive back is a broad term that describes cornerbacks and safeties. These are the deeper or “secondary” defenders. If you break the position down to its main responsibility, it sounds simple.

Speed is a major asset that prevents defensive backs from getting outrun by wide receivers, but it isn’t the only important quality. It also takes quickness, agility and flexibility in the hips to quickly break on passes and change directions in an instant.

“You want to be like Spider-Man,” Cary-Grove defensive coordinator Don Sutherland said. “Your senses have to be tingling the whole time you’re on defense if you’re going to be a good defensive player.”

Cornerbacks and safeties have similar responsibilities. Both have to cover receivers and help in run support. But there are some distinct differences.

Sutherland said that, to him, cornerbacks are like the basketball players. They have to be good in the open court and able to make plays in the air. By contrast, his linebackers are more like wrestlers — quick on their feet and aggressive.

The safeties are like a hybrid between the two positions — fast, strong, smart, tough and aggressive. While corners are mainly focused on covering receivers, safeties have to also be a factor in stopping running plays and making tackles in the open field.

“The guys who could be wrestlers, but play basketball,” Sutherland said.

The combination of these two somewhat contradictory skill sets makes finding a good safety a difficult task for defensive coaches. But as offenses continue to evolve, it’s becoming more important than ever to have this type of dynamic playmaker.

Sutherland used to tell his free safety to sit back in center field and only worry about long passes. “If you don’t have to make a tackle all year, you’ve had a good year,” he said.

Now?

“You’ve got deep middle, AND you better be making tackles on the line of scrimmage,” he said.

It’s a tough task. It takes the right breed of athlete to ace this test.